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doc: editorial tweaks to "Real-Time (RT) Performance Analysis on ACRN" 

Editorial tweaks to the "Real-Time (RT) Performance Analysis on ACRN" document,
mostly to improve readibility, no technical content change.

Signed-off-by: Geoffroy Van Cutsem <geoffroy.vancutsem@intel.com>
This commit is contained in:
Geoffroy Van Cutsem 2019-09-25 16:54:53 +02:00 committed by deb-intel
parent 7eb0dc1436
commit 9c273cf33e
1 changed files with 24 additions and 23 deletions
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47
doc/tutorials/realtime_performance_tuning.rst
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@ -1,20 +1,20 @@
.. _rt_performance_tuning:
Trace and Data Collection for ACRN Real-Time (RT) Performance Tuning
####################################################################
Real-Time (RT) Performance Analysis on ACRN
###########################################
The document describes the methods to collect trace/data for ACRN RT VM
The document describes the methods to collect trace/data for ACRN Real-Time VM (RTVM)
real-time performance analysis. Two parts are included:
- Method to use trace for the VM exits analysis.
- Method to collect performance monitoring counts for tuning based on Performance Monitoring Unit, or PMU.
- Method to trace ``vmexit`` occurences for analysis.
- Method to collect Performance Monitoring Counters information for tuning based on Performance Monitoring Unit, or PMU.
VM exits analysis for ACRN RT performance
*****************************************
``vmexit`` analysis for ACRN RT performance
*******************************************
VM exits in response to certain instructions and events are a key source of
performance degradation in virtual machines. During the runtime of a hard
RTVM of ACRN, the following impacts real-time deterministic latency:
``vmexit`` are triggered in response to certain instructions and events and are
a key source of performance degradation in virtual machines. During the runtime
of a hard RTVM of ACRN, the following impacts real-time deterministic latency:
- CPUID
- TSC_Adjust read/write
@ -22,13 +22,13 @@ RTVM of ACRN, the following impacts real-time deterministic latency:
- APICID/LDR read
- ICR write
Generally, we don't want to see any VM exits occur during the critical section of the RT task.
Generally, we don't want to see any ``vmexit`` occur during the critical section of the RT task.
The methodology of VM exits analysis is very simple. First, we clearly
The methodology of ``vmexit`` analysis is very simple. First, we clearly
identify the **critical section** of the RT task. The critical section is
the duration of time where we do not want to see any VM exits occur.
the duration of time where we do not want to see any ``vmexit`` occur.
Different RT tasks use different critical sections. This document uses
the cyclictest as an example of how to do VM exits analysis.
the cyclictest benchmark as an example of how to do ``vmexit`` analysis.
The critical sections
=====================
@ -46,32 +46,33 @@ Here is example pseudocode of a cyclictest implementation.
next += interval
}
Time point ``now`` is the actual point at which the cyclictest is wakeuped
Time point ``now`` is the actual point at which the cyclictest app is woken up
and scheduled. Time point ``next`` is the expected point at which we want
the cyclictest to be awakened and scheduled. Here we can get the latency by
``now - next``. We don't want to see VM exits during ``next`` through ``now``. So, define the start point of critical section as ``next`` and end
point ``now``.
``now - next``. We don't want to see any ``vmexit`` in between ``next`` and ``now``.
So, we define the start point of the critical section as ``next`` and the end
point as ``now``.
Log and trace data collection
=============================
#. Add timestamps (in TSC) at ``next`` and ``now``.
#. Capture the log with the above timestamps in the RTVM.
#. Capture the acrntrace log in the service VM at the same time.
#. Capture the ``acrntrace`` log in the Service VM at the same time.
Offline analysis
================
#. Convert the raw trace data to human readable format.
#. Merge the logs in the RTVM and the ACRN hypervisor trace based on timestamps (in TSC).
#. Check to see if any VM exit exists within the critical sections. The pattern is as follows:
#. Check to see if any ``vmexit`` occured within the critical sections. The pattern is as follows:
.. figure:: images/vm_exits_log.png
:align: center
:name: vm_exits_log
Performance monitoring counts collecting
****************************************
Collecting Performance Monitoring Counters data
***********************************************
Enable Performance Monitoring Unit (PMU) support in VM
======================================================
@ -167,10 +168,10 @@ exported by recent versions of the Linux kernel.
Refer to https://github.com/andikleen/pmu-tools for pmu usage.
Top-down Micro-architecture Analysis Method (TMAM)
Top-down Micro-Architecture Analysis Method (TMAM)
==================================================
The Top-down Micro-architecture Analysis Method (TMAM), based on Top-Down
The Top-down Micro-Architecture Analysis Method (TMAM), based on Top-Down
Characterization methodology, aims to provide an insight into whether you
have made wise choices with your algorithms and data structures. See the
Intel |reg| 64 and IA-32 `Architectures Optimization Reference Manual <http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-optimization-manual.pdf>`_,